Electrical discharge device



Oct. 7, 1941. E. D. MOARTHUR 2,258,254

ELECTRICAL DISCHARGE DEVICE Filed June 29, 1939 Inventor:

E'lmerD. Mc Arthur; I

by JV j His Attorney.

Patented Oct. 7, 1941 ELECTRICAL DIS CHARGE DEVICE- Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 29, 1939, Serial No. 281,865

15 Claims.

This invention relates to electrical discharge devices and to improved methods and means for controlling electron discharge currents. While not limited thereto, the invention is particularly useful in its application to amplifiers, detectors, oscillators and converters for use at Wave lengths downv to 5 centimeters.

Inasmuch as an adequate explanation of the invention necessarily involves the repeated use of. terms of a more or lessitechnical character, I have .in the following paragraphs set forth the meanings which I desire to attach to certain such terms.

By conduction current I intend to designate a stream of moving charges, such, for example, as an electron beam current passing through an evacuated or gas-filled conduction space.

By conduction current modulation I mean to designate the controlled production of irregularities in a conduction current stream. Thus, a conduction current modulated electron beam is a beam in which at any given time systematic irregularities in electron velocity or electron density exist from point to point along the beam. Likewise at any given point systematic changes occur with respect to time.

In conventional electronic vacuum devices the control member or grid is ordinarily so constructed and arranged as to affect directly the electron emission from the cathode, thus producing a type of conduction current modulation? as, hereinbefore defined. It may be shown that the conduction current variations soproduced by the grid have the efi'ect of inducing a similarly varying current in the grid circuit. Under ordinary conditions and at low frequencies this induced current, which is caused by instantaneous differences inthe electron charges approaching and receding from the grid, is relatively, small and is approximately 90 degrees out of phase with the grid voltage,.so that it produces no appreciable power loss. I-Iowever, as the operating wavelength is decreased so that the electron transit time becomes appreciable with respect to the reciprocal frequency (1/1) of the control grid potential variations, the induced current not only increases but becomes more nearly phase with the grid voltage. These two effects combine to produce the result that the apparentshunt resistance of the grid circuit varies inversely as the second power of the frequency of the operating voltage. It is for this reason that at very high frequencies (1. e. very short wave lengths) the conventional type of, grid attains such a low shunt impedance and involves such .a large power loss as to be practically unusable. c. It is a primary object of my invention .to pro--. vide an improved method and means for con-, trolling an electronic discharge current whereby the impedance of the control circuit is main-,- tained at a high value even whencontrol poten-. tials of very short Wave lengths are involved, In this connection, it is proposed to provide, means to compensate for or neutralize the effects of power flow from the control circuit into the dis charge stream. More specifically, it is proposed to provide means associated with the contrpl circult for returning to such circuit fromthe discharge stream power equivalent to that which is taken by the stream from the control means. In a particular embodiment of the invention, the means utilized tofaccornplish the foregoing ends includes a multipart control electrode structure and circuit elements so associated therewith as to cause voltage variations produced in'one part of the electrodestructure to beaccompanied by compensatory fyariationsof opposite phase in another part of thes'tructure. Aswfllbeimore fully explained hereinaftenthis expedientmini mizes the effect at the control voltagesource of power flow produced in the various Parts-'offthe electrode structure as a result of passage there through of the modulated discharge stream. t The novel featureswhich I believe tobe char-'- acteristic of my invention are set forth with par ticularity in the appended claims. My invention itself, however, both as to its organizationi'and" method of operation, together with further-"ob- Jects and advantages thereofmay best be understood by reference to the following description taken in' connection with the accompanying drawing in which Fig. l is a circuit diagram representing one form of my invention; Fig, 2 represents a circuit which is a modification of the circuit of Fig. 1; Fig. 3 illustrates an electron. discharge device of a modified type in a circuit similar to that of 'Fig'. 2; Fig, 4 representsanother electron discharge device of a modified type; Fig. 5 represents still another electron dis charge device of, modified form with a1 slightly difierent circuit; and Fig. 6 illustrates a different type of circuit embodying my invention; j

Referring to .Fig. 1, I have shown a circuit embodying one form of my invention. In this circuit an electron discharge device ID has, a cathode I I connected to a suitable source 63 of' grid bias voltage. The source 63 is shunted. by a by -passing condenser 64 and is connected to one; side of thesecondary of a transformer [2, .to the primary of which any desired source of ultra high frequency voltage may be applied. The other side of the secondary of transformer I2 is connected to one side of a condenser I3 which connects together the ends of a transmission line which has distributed inductance and capacity. This condenser I3 acts as a high frequency shortcircuiting termination for the transmission line. The transmission line with the attached elements forms a balanced circuit tuned to the ultra-high frequency Wave applied to the transformer I2 and includes a pair of parallel conductors I4 and I5, each having one end connected to a terminal of condenser l3 and the other end connected to one of two control elements of the electron discharge device I0. A first control grid I6 is connected to the conductor I4, and a second grid I1 is connected to the conductor I5. The grid I6 must be more effective to produce charge density modulation of the electron stream than grid I"! in order that the latter grid may not neutralize the modulating effects of the former. In the arrangement shown in Fig. 1, this action is assured by the fact that the grid I1 is substantially shielded from the cathode by the interposition of the grid I6, so that it can produce relatively little variation in the cathode emission. A suitable source of direct current potential I8 may be connected across condenser IS in order to vary the transit time of electrons between the grids I6 and IT. The anode I9 of the electron discharge device I is connected through the primary of a transformer 20 to a suitable source of operating potential 2| which is connected to the cathode II. The source 2| is shunted by a by-passing condenser 22. The secondary of the transformer 20 may supply ultra high frequency power to a load device, such as an antenna or the like.

In the operation of this circuit, when either charge density or velocity of the conduction current on the cathode side of the grid I6 is different from the charge density or velocity of conduction current on the other side of grid I6, there is a net current induced in the conductor I4 by this difierence. In the associated network this induced current divides itself among the available conductive paths in accordance with their respective impedances. There is a similar current induced in the grid I1 and the conductor I5. These currents tend to result in power flow from the transformer I2 to the electron stream and thus objectionably to lower the apparent input impedance of the tube.

In order to reduce this power flow to a minimum, my present invention makes use of the principles described in the following. Assuming that the currents induced in the grids I6 and I! are equal and of the same phase, it is obvious that the resulting power flow to the external circuit will be zero only if the relative variations in the grid voltages with respect to the cathode I I are equal and of opposite phasein which case power neutralization will occur. To carry this principle into eifect, the transmission line which comprises conductors I4 and I terminated by the condenser I3 may be so adjusted as to make the currents in grids I6 and I! produce power flow such that the net power supplied to grids I6 and I! by transformer I2 is a minimum.

The above conclusions have been based on the simplifying assumption that the two grids I6 and I1 occupy the same position in space. Although this condition obviously cannot be realized in practice, the consequences of its non-fulfillment may be minimized by the use of the potential source I8 so poled as to decrease the transit time of electrons between grids I6 and I1. There are, of course, definite physical limitations on the amount of voltage which one may apply between two such electrodes. Also, the effect of the lack of space coincidence between grids I6 and I1 is such as to make the currents varying, or alternating, in those grids differ not only in magnitude but in phase. Therefore, means allowing accurate control of both phase and magnitude relation between the voltages varying, or alternating, on the two grids may be used to insure that not only the flow of real power but the flow of reactive power produced by the varying current in grid I6 is equal and opposite to that in grid H.

The transmission line comprising conductors I4 and I5 as shown in Fig. 1 operates to produce a voltage variation on grid I! with respect to cathode II which is substantially in opposite phase with respect to the voltage variation on grid I6. The power flow in grid I! may therefore be considered as directed from the stream into the grid, so that in grid It the power flow may then be considered as directed from the grid into the stream, as in fact it appears to be. I wish to make it clear that by the term opposite phase as used herein and in the appended claims I intend to indicate the condition in which the voltages on grids I6 and I I are at any angle greater than degrees and less than 270 degrees as may be required to produce substantial neutralization of power flow.

The two grids I6 and I! may conveniently be viewed as two parts of a unitary electrode structure employed to produce conduction current modulation of the electron stream. This unitary structure is excited from the transformer I2 so that its alternating voltage with respect to cathode II is that of the high frequency potential in transformer I2. The transmission line, which may also be considered as part of the control means, is the agency which causes the potential on grid I? to vary in substantially opposite phase with respect to the alternating potential on grid The operation of the device illustrated by Fig. 1 may be analyzed by considering the action of the control grids I6 and I1 separately. An ultra high frequency wave impressed on the transformer I2 changes the potential of the grid I6 with respect to the cathode II. At the instant when the grid I6 is most negative, the effect of the grid on the cathode is to reduce emissivity to a minimum and to assure the release of an electron group of minimum density. During the approach of this minimum density electron group to the grid I6 it is decelerated by the negative potential of the grid. The same electron group of minimum density is then accelerated during its recession from the grid I6, because the grid is, by assumption, still negative. The acceleration during recession is less than the deceleration produced on approach, because the potential of the grid I6 is steadily becoming less negative. This electron group, therefore, suffers a net deceleration and delivers power to the grid I6.

At a later instant of time, that is, when the grid I6 is. least negative in potential, an electron group of maximum charge density is emitted from the cathode II. During the time of travel of this maximum density electron group toward and past the grid, the potential of the grid I6 is becoming more negative} There is a deceleration experienced by this maximum density electron group in approaching the grid- IE, but in this case a-greater amount of acceleration is experienced by this same group in receding from the grid It 7 (since the negative potential thereon is becoming more negative). 'The maximum density electro'n group, therefore, experiences a net acceleration and takes power from the grid I6.

From the'fo'regoing it will be seen that while electron groups of minimum density deliver power to the grid I6, electrong'roups of maximum 'densitytake power therefrom. Due to the greater amount of energy represented by the change in condition of the latter groups, there is a net power loss to the stream. This power loss obviously must be supplied by the input circuit, a circumstance which is highly undesirable since the loadthus imposed on the input circuit may at extremely high frequencies exceed the power available for driving the input circuit. It will now be shown that provision of the grid I'I,-excitedin proper phase and at the-same frequency as the grid It, results in an overall reduction of thisundesirable loss from the input circuit. Considering the electron stream moving toward the grid H from the grid I6, it may be seen from what has been said above that the nature of the stream is that of a continuous suc- 'cession of electron groups whose density varies from point to point along the stream. Let it now be assumed that some 'mechanism (e. g., the transmission line I4, I in Fig. 1) causes the potential of the grid IT to vary in such fashion that the grid I1 is least negative in potential at the instant when an electron group of minimum electron density is approaching (this being opposite to the condition above postulated as prevailing at the grid I6 during the approach of the same electron group to such grid). Under such conditions, during the entire period when the above noted electron group is under the influence of the grid H, the grid is obviously increasing in negative potential. The electron group, therefore, is decelerated on its approach to the grid I1, but. is accelerated a greater amount during its recession therefrom. It, therefore, undergoes an overall acceleration, and thus takes power from the grid I'I.

An electron group of maximum density subsequently approaches the grid I! when its potential is most negative and passes the grid H as its potential is becoming less negative. This second group is decelerated upon approaching the grid H, but during recession of the group is accelerated a lesseramount due to the decreasingly negative potential of the grid I'I. Ihis large electron group, therefore, undergoes a net deceleration, which is greater than the net acceleration experienced by the previously considered small electron group. More power, therefore, flows from the electron stream'to the grid I'I than from the grid I! to the stream. The grid II consequently abstracts power from the electron stream.

i Considering the action of the two control grids I6 and- H together, it will be seen first that the control grid I 6 produces a modulation of the electron stream, with concurrent power flow from the input circuit through the grid IE to thestream, and second that the grid I1 abstracts power from the electron sltream- -this condition obtaining as long asproper phase relationship is maintained between the potentials of the two grids. A result of the common excitation of the two grids I6 and I1 and the maintenance of the proper phase relationship between them as described above is'to provide a neutralization of power losses in the input circuit. As an ultimate consequence the net power, averaged over each cyolecf the high frequency potential exciting the two grids Ifiand H, which power must be suppliedto the input circuit (e. g., from a signal source), may be materially reduced.

It is the function of the transmission line I4, I5 of Fig. 1 to maintain the above specified phase relationship between the two grids I6 and I1, and it may be observed that the excitation of this transmission line is another result of .abstraction of power from the stream by grid I'I. As has been noted at an earlier point herein, the resonant frequency of the transmission line shall be the same as the impressed signal frequency; whereby the lineis capable of being excited by power taken by the grid H from the electron stream, which is modulated at the same frequency as that of the impressed signal.

In Fig. 2 there is shown a modification of the circuit shown in Fig. 1. In the new figure such elements as are identical with those previously described are indicated by like reference characters. An additional grid 23 which functionsas a third or screen grid is shown between the grid I1 and the anode I9. This screening electrode 23 is connected through a suitable portion of the potential source ZI to the cathode II. A bypassing condenser 24 connects the grid 23 to cathode II. By the use of this screen grid variations in impedance or other characteristics of the transformer 20 and the connected apparatus do not affect the value of the currents which flow in grids I6 and I1. Compensation of the power flows in these grids is maintained unaifected and undesired oscillations caused by fortuitous coupling between the input and output circuits are prevented.

In Fig. 3 amodification of the discharge device indicated in Fig. 2 is shown with its circuit, the device being of the electron beam type. In the new figure such elements as are identical with those previously described are similarly numbered. The envelope 25 contains an electron gun generally designated 26 which includes an indi rectly heated unipotential electron emission surface 21. A control grid 28 arranged as a oylin der on the same axis as the cathode 21 produces charge density modulation of the electron stream. This grid 28 is connected to conductor It as was grid I6 in Fig. 2. The grid 28 is not contiguous to the'electron stream, however, and will, therefore, have little current produced therein due to collection of electrons from the stream. A second grid 29 also arranged as a cylinderori the same axis, is connected to the conductor l5 and functions in the same way as thegrid I! described above in connection with Fig. 1. In other words, the transmission line comprising conductors I4 and I5 is connected between grids 28 and 29 and is tuned so as to require grid 29 to oscillate with a Voltage in opposite phase to any voltage oscillations induced upon the grid 28 by variations in amount of conduction current passing therethrough. A screen grid 39, which is also a cylinder on the same axis, is connected to condenser 24 and a tap'on source 2I, and functions in the same wayas'the grid 23 in the circuit of Fig. 2. An anodeSI' isplaced so as to be influenced by the electrons after-pas-,

sage of the cathode past all three of the-grids. It may be found desirable to make the -g'rid 28 very long so-that the voltage variations of grids 29 and 30 and of the anode 3I do not appreciably afiect the field at the cathode 23. The grid 29 may thereby conveniently be prevented from producing any substantial conduction current modulation.

In the figure under consideration the circuit is modified slightly to provide means for controlling the magnitude relation between the voltage on grid 28 and that on grid 29. The connection from the transformer I2 to the transmission line is made adjustable along one of the conductors. By adjusting this connection more voltage may be induced upon one grid than on the other. Since this adjustment introduces a possibility of radiation from the unbalanced transmission line, the line may be shielded to prevent undesired radiations from affecting other parts. By thus varying the voltages on the two grids the power flows may be more nearly equalized, since the two grids may have diiferent amounts of current. If complete control of both phase and magnitude of these voltages is desired, it may be necessary to employ transmission lines terminated in their characteristic impedances.

Referring to Fig. 4, I show a form of tube slightly modified from that shown by Fig. 3. An envelope 25 contains electrodes which are identical in function with those shown in Fig. 3. However, the grids 28 and 29 are replaced by torus-shaped grids 32 and 33. The torus-shaped grid 32 is arranged axially with respect to the cathode and to the conduction current flowing therefrom, and the ring grid 33 is likewise placed axially therewith. Since grid 33 affects the field at the cathode 21 to some extent, a positive bias may be applied to itto act as an accelerator electrode. These grids 32 and 33 function in the same way and may have the same connections as those illustrated in Fig. 3.

Referring to Fig. 5, there is shown a form of tube which is modified from that shown by Fig. 3 in such a way that the second grid has the same capacity with respect to the cathode as does the first grid. Such elements as are identical with those of Fig. 3 are given like reference numerals. The torus-shaped grid 32 is disposed adjacent the cathode or electron stream source 26 and a grid 34 is placed so that it has little effect on the electric gradient adjacent the oathode. The lead from grid 32 through the envelope 25 is considerably removed from the lead to the cathode 27. The lead from grid 34 is placed near the lead from the cathode 21 as it passes through the envelope 25. By such construction the efiective capacity from each grid to the cathode may be made equal. These capacities should be equal on the assumption that the alternating voltages on these two grids are equal. If the voltages are unequal, of course, the capacities should be made unequal in an opposite sense.

By such an arrangement of elements the flow of current in the cathode 21 due to voltages induced on grid 32 by passage of the conduction current modulated electron stream thereby is prevented by the fact that grid 34 induces a voltage on cathode 2'! of about equal magnitude and of opposite phase to that induced on the cathode by grid 32. This form of construction may be of great advantage in aiding efficient construction of the circuit connections for electrode gun 26. the capacities from grids 32 and 34 with respect to the screen grid 30 may at the same time be made such that no voltage is induced in the screen grid due to Voltage variations on the grids 32 and 34.

By placing the leads as shown,

In the figure under consideration, a somewhat different circuit from those shown in Figs. 1 to 3 is used to provide voltages for the two grids forming the control structure. Instead of a quarter wave transmission line, a tuned circuit including capacity 35 and inductance 36 is connected between the grids 32 and 34. An adjustable tap on the inductance 35 is connected to cathode 2'! through a source 31 of grid bias voltage shunted by a lay-passing condenser 38. Signal voltage is applied to a coil 39 which is inductively coupled to inductance 36. In operation, as before, the grids 32 and 34 are operated at potentials of opposite phase and of magnitudes such as to produce equal and opposite power flows in the two grids.

Referring to Fig. 6, a modified type of circuit is shown which utilizes a tube adapted tooperate in push-pull relation. Th circuit includes an input transformer 40 which has its primary energized by ultra-high frequency voltage. The secondary has a center tap connected through a source of potential 4| to ground. A by-passing condenser 42 shunts the source of potential 4|. A condenser 43 in shunt to the secondary of transformer 43 tunes the secondary to the ultrahigh frequency voltage applied to the primary. An electron discharge device 44 includes two conduction current paths and is shown as otherwise similar to the device of Fig. 1 for convenience. This device, if used for very high frequencies, is preferably constructed as an electron beam tube, as shown by Figs. 3, 4 and 5. The two cathodes 35 and 46 are connected to ground. The respective first grids M and 48 are connected to the two ends of the secondary of transformer 53. The respective second grids 49 and 53 are cross-connected to the opposite first grids by condensers 5| and 52. The third grids 53, which are screen grids similar to grid 23 or 30, are connected through a source of bias potential 54 to ground. This source of bias potential 54 is shunted by a by-passing condenser 55.

The anodes 56 and 51 are connected to the opposite ends of a tuned circuit which comprises a condenser 58 and the primary 59 of an output transformer. A suitable source of anode operating potential is connected to the center tap of the primary 59. A secondary 60 of the output transformer may supply ultra-high frequency power to any device such as an antenna or a subsequent stage of amplification. Choke coils BI and E2 connect the respective grids 49 and to suitable sources of bias voltage.

This circuit is a balanced modification of the circuit of Fig. 5 and its construction permits a very convenient circuit arrangement. Since it is a push-pull circuit in which the device is connected, the second grids 49 and 50 are supplied with voltage substantially opposite in phase to that on the first grids by coupling these second grids to the opposite side of the push-pull circuit. Viewed alternatively, the power fed to one electron stream b grid 4: is abstracted from the other stream by grid 53 and fed to grid 4'! by condenser 52. Likewise, the power taken by grid 49 from the stream is supplied to grid 48 by condenser 5!.

While I have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto, since different modifications ma be made both in the circuit arrangement and instrumentalities employed, and I contemplate by the appended claims to cover any such modifications as fall fective therefor, asource of high frequency DO? tential, means to vary cophasally the potentials of both saidelectrodesin accordance with the high frequency potential variations of-said source to produce conduction current modulation of said stream, and means-to cause current variations in saidelectrodes produced by the conduction modulation of said stream to effect oppositely phased potential variations of: said electrodes at the frequency of said'high-frequency potential, whereby'the effect at said source of power flow in the first electrode resulting from current induced. therein due to the modulation of the stream :is substantially neutralized by the efiect of power; flow in saidj'secondi electrode from similar causes.

2. In combination, an electron discharge. device having means including a cathode for producing a stream of electrons, a source of high frequency potential, and control meansexoited from said source including a first and a second part arranged to be traversed by said. stream,

said first part being effective to produce conductioni current modulation of said stream in accordance with the high frequency potential variations of said source, and said second'part being relatively less effective to produce such modulation, and means to. cause" current variations in said parts produced by the conduction current modulation of said stream to effect'oppositely phased potential variations of said parts at the frequency of said high frequency potential to minimize the effect at said source of power fiow to the respective parts of said control means due to current induced therein as a result of the modulation of said stream.

3. In. combination; an electron" discharge devicev having means including a cathode for producing a; stream of electrons, a source of high ffequencypotentialgand control means excited fromzsaid source to produce conduction current modulation of said stream, said control means includinga'first'and 'a second part arranged to be'traversed by said stream, said first part being effective and said second part less effective 'to 'produce' conduction current modulation of said stream in accordance with the high frequency potential'variations of said source, and a tuned circuit connectedibetweensaid first and second 'parts to cause current variations in said parts produced by the conduction current modulation ofsaid stream to effect oppositely phased potential variations of said parts at the frequency of said high frequency potential to' minimize the effect at said source of power flow in therespective parts of said control means due to current induced therein as a result of the modulation of said stream.

4. In combination, an electron discharge device having means including a cathode for producing a stream of electrons, control means including a first and a second electrode arranged to be traversed by said stream, a source of high frequency potential connecting said control means. to .said cathode,;said first ielectrode being effective to. p roduce conduction current modulation of said stream in accordance with the high frequency potential-variations of said source and said second: electrode being lessefiective therefor, and-a standing wave ,transmission line connecting. said electrodes to causecurrent varithe modulation of said beam.

ationsin said electrodes produced by; the conduction current modulation ofisaid stream-to effect oppositely phased potential variations'of said electrodes at the frequency; of said. high frequency potential to minimize the effect-at said source of power flow in'said electrodesdue to. current induced therein as a result of modulation of said stream.

5. In combination, an electron discharge device having meansfincluding a cathode and an anode for producing a stream of electrons, a source of. high frequency potential, control means excited from said source .to' produce conduction current'modulation of saldstream inaccordance with the high frequency, potentlalvariation's of said source, and means near said anode to'prevent' appreciable coupling" between said' anode and said control means; said control means in cluding. a'first'and. a second part arranged to be successively, traversed by said stream, and means to cause current variations in said parts produced by the conduction current modulation of saidstream to effect oppositelyphased'potential;variations of said. parts at the frequency of said. high frequency; potential; to. minimize. the effect at .said source'of power flow-1n the respective parts'of said control zmeans due to current induced therein as a result of the modulation of said stream.

6. In combination, an electron discharge .device having means including a, cathode for. producinga beam of electrons; a source of high frequencypotential, and control means excited from said source to produce conduction current modulation of said beam in accordance with the high frequency potential variations of said source, said control means including a first and a second part arranged-adjacent but not con sitely phased potential-variations of said parts 'at the frequency of said high frequency potential to minimize the effect at said source of power flow in the respective parts of said co'ntrol means due to current induced therein as a result of 7'; In c'ombinatiom'an electron discharge device having means including a cathode for producing 'a stream of electrons, a first electrode and a second electrode arranged to be traversed by the stream, said first electrode being effective, when subjected to varying potential, to'produce conduction current modulation of said. stream and said second electrode being less/effective therefor, a source of high frequency. potential means for exciting saidJelectrodesfrom said source'to'produce conduction current modulation "of i'saidi'strea'm in accordance withz'thehigh frequencyipotential variations'of saidsource, and

means connected to'saidsource to cause'oppositely phased potentialyariations ofsaid electrodes at the frequency of said high frequency potential, which variations, by reason of similarly phased varying currents induced in said electrodes by the conduction current modulation of said stream, minimize the effect at said source of power flow in said electrodes due to passage of the modulated electron stream thereby.

8. In a control means for producing conduction current modulation of an electron stream at a predetermined frequency, said control means including two portions arranged to be traversed by said stream, one portion being efiective to produce conduction current modulation of said stream, the method of minimizing power flow in said control means which comprises causing the respective voltages of said portions to vary at said frequency in substantially opposite phase with respect to each other.

9. A method of operating a discharge device having means for producing an electron stream and a pair of control electrodes arranged to be traversed successively by the stream, which method comprises varying the potential of one of said electrodes at high frequency to produce conduction current modulation of the stream, and causing the respective voltages of said electrodes to vary at said frequency in substantially opposite phase with respect to each other.

10. A method of operating a discharge device having means for producing an electron stream and a pair of control electrodes arranged to be successively traversed by the stream which method comprises causing the voltage of the first of said control electrodes to vary at a high frequency to produce conduction current modulation of the stream such that currents are induced in said electrodes by conduction current variations in the stream, and causing the respective voltages of said electrodes to vary at said frequency in substantially opposite phase with respect to each other to equalize the power flow in the pair of electrodes.

11. The method of producing conduction current modulation of an electron stream by means of a pair of control elements adjacent the stream, which method comprises varying the voltage of one of the elements at high frequency to produce conduction current modulation of the stream and varying the voltage of each of the pair of elements at said frequency in opposite phase with respect to the voltage of the other element to minimize the power flow into said stream from the elements.

12. In electronic apparatus, means for producing a stream of electrons, a modulating electrode traversed by said stream, means including said electrode for modulating the stream at a frequency at which the phase relationship between current induced in the electrode by reaction of the modulated stream thereon and the potential by which the modulation is produced is such as to cause objectionable power loss in said modulating means, a second electrode which also forms a part of said modulating means and which affects said stream and is affected by it in a manner similar to said first electrode, and means for causing potential variations of said second electrode to occur at said frequency and in a predetermined phase relationship with respect to the current induced in said second electrode by the electron stream, said predetermined relationship differing from the phase relationship first mentioned above by approximately one hundred and eighty degrees, whereby said objectionable power loss is minimized.

13. In combination in electron discharge apparatus for operation at high frequencies, a cathode, an anode for receiving an electron discharge stream from said cathode, control means positioned between said cathode and anode for producing charge density modulation of said stream, a source of high frequency potential, means for impressing said high frequency potential upon said control means, whereby said control means tends to transfer power from said source to the discharge stream, said control means having separated portions and one of said portions being more effective than the other to produce charge density modulation of said stream, and means for maintaining net power fiow in one of said portions opposite the net power flow in the other portion averaged over each cycle of said high frequency potential, thereby to minimize the net power transfer from said source to said stream while maintaining the effectiveness of said control means to produce charge density modulation of the stream.

14. In combination in electron discharge apparatus for operation at high frequencies, a cathode, an anode for receiving an electron discharge stream from said cathode, means including two control electrodes positioned between said cathode and anode for producing charge density modulation of said stream, one of said electrodes being more efiective than the other to produce such charge density modulation, a source of high frequency potential, means for impressing said high frequency potential upon said control electrodes, whereby said control electrodes tend to transfer power from said source to the discharge stream, and means for maintaining net power flow in one of said control electrodes opposite the net power flow in the other control electrode averaged over each cycle of said high frequency potential, thereby to minimize the net power transfer from said source to said stream while maintaining the effectiveness of said two control electrodes to produce charge density modulation of the stream.

15. In combination in electron discharge apparatus for operation at high frequencies, said apparatus having means including a cathode for producing a stream of electrons, control means including two separated portions for producing charge density modulation of said stream, one of said portions being'more effective than the other for producing such modulation, a source of high frequency potential, means to vary the potential of said portions in accordance with the high frequency potential variations of said source to produce charge density modulation of said stream, whereby said control means tends to deliver power to said stream, and means to maintain net power flow in one of said portions opposite the net power flow in the other portion averaged over each cycle of said high frequency potential, thereby minimizing the effect on said source of power flow in said electrodes while maintaining the capability of said two portions to produce charge density modulation of said stream.

ELMER D. MoARTHUR. 

